Method of manufacturing a shape from a composite material

ABSTRACT

A method of manufacturing a shape from a composite material by applying laminations impregnated with plastic resin to a positive mold. At least one cellular, cellular-core layer is applied into the neutral zone of the laminations and embedded into them while the laminations are being built up. The cellular layer is a rigid foam. The cellular-core or honeycomb layer has the axis of each cell radial to that of the shape and can be single, double, or multiple. If double or multiple it may have an interior connective layer consisting of plastic, foil, glass cloth, non-woven carbon-fiber fabric, polyimide, or woven or non-woven fabric impregnated with plastic resin. The cellular-core or honeycomb layer is intended to make the shape more stable and flexurally strong.

This application is a continuation of application Ser. No. 562,687,filed Dec. 19, 1983, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to a method of manufacturing a shape froma composite material by applying laminations impregnated with plasticresin to a positive mold.

Similar methods of manufacturing a shape from a composite material andshapes manufactured in accordance with such a method are known fromEuropean Patent Application No. 79 103 881.3.

The advantages of shapes manufactured in accordance with such a methodare that they are relatively strong and can be manufactured with littlecapital outlay on a light-industrial scale. The drawback thereof is thatthey will often not support enough load, especially in compression andflexural strength.

SUMMARY OF THE INVENTION

The object of the present invention is an improved method of theaforesaid type for manufacturing shapes that will firmly support a loadwhile remaining light in weight.

This object is achieved in accordance with the present invention whereinat least one cellular, cellular-core layer is applied into the neutralzone of the laminations and embedded into them while the laminations arebeing built up. Preferably, the axis of each cell of the cellular-corelayer is disposed radially of the axis of the shape.

The method in accordance with the invention now makes it possible tocreate a shape that, while it differs hardly at all in weight from knownshapes, can support considerably more load. Its cellular-core layerprovides, as a result of being embedded in the laminations, a stableframework that considerably increases in particular the transversestability of the shape as will as its flexural strength.

In other and preferred embodiments of the present invention, thecellular-core layer can be multiple, preferably double. The multiple ordouble layer can manufactured as and inlaid between the laminations as aunit. The multiple or double layer can have a connective layer betweeneach cellular-core layer. The connective layer can be made of plastic,foil, glass cloth, non-woven carbon-fiber fabric, polyimide, or woven ornon-woven fabric impregnated with plastic resin. The cells in theindividual cellular-core layers can be of different sizes. Thedimensions of the cells in the individual cellular-core layers canincrease from the positive mold outward. The cellular-core layer can beembedded into the laminates bent into a tube and abutting. Thecellular-core layer can be in the form of strips and inlayed in thelaminations with its edges adjacent or in the form of a helix. Thecellular-core layer can be inlaid in the laminations in the form of aspiral. At least one, also spiral, lamination can be inlaid between thespirals.

Subsequent to laying a first lamination in the form of an innersupporting layer and/or shell layer on the positive mold or core and toapplying a single- or multiple-lamination cellular-core layer, anotherlamination in the form of an outer shell layer can be applied. Thefinished layered structure can be secured by a coil of compression tapethat is removed subsequent to curing. The coil can consist of polyamidetear-off tape.

In one embodiment of the invention an initial lamination in the form ofan inner supporting layer of glass fibers, glass cloth, glass knit, orglass plait is stretched over or wrapped around a positive mold, aninner shell layer consisting of parallel carbon fibers is applied, andanother lamination in the form of an outer shell layer consisting ofparallel carbon fibers and an outer supporting layer consisting of glassfibers, glass cloth, glass knit, or glass plait are stretched over orwrapped around the cellular-core layer. The laminations can be appliedimpregnated with plastic resin and still wet. The positive mold canconsist of plastic-covered foam. The parallel carbon fibers can beapplied parallel to the axis of the shape. One of the layers, preferablythe outer layer of the double or multiple layer, can have an undulatingsurface. The cellular-core layer can be made of an extruded materialsliced into flexible sheets. The cellular-core layer can be made ofcorrugated or folded strips of foil cemented or hot-bonded together.

The cellular material comprises at least one layer of a rigid foam, suchas polyurethane, polyvinyl chloride, polyacrylic, polystyrene, epoxide,polyethylene or polyester foam and is embedded into the neutral zone ofthe layers. The rigid foam can be closed- or open-pored or closed- oropen-celled, preferably medium-pored. It can be in sheers or strips. Itcan also be introduced in the form of liquid components and only foamedin situ into or onto the semifinished shape.

Some preferred embodiments of the invention will now be described withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a shape in accordance with theinvention from which the layers have been removed to different depths toshow them more clearly,

FIG. 2 is a section through a shape in accordance with the inventionillustrating one type of layer that can be embedded,

FIGS. 3 and 4 illustrate one way of constructing a positive mold,

FIG. 5 illustrates the first step in the method, which is to apply thefirst lamination to the mold,

FIG. 6 illustrates the further buildup of a possible embodiment,

FIG. 7 illustrates the application of the second lamination--the outersupporting layer--to the mold,

FIGS. 8, 9 and 9a illustrate various embodiments of the layers,

FIG. 10 is a schematic section through the layer of FIG. 8,

FIG. 11 is a section through a double layer,

FIGS. 12, 13, and 14 illustrate various embodiments of shapesmanufactured in accordance with the invention,

FIG. 15 illustrates a shape in accordance with the invention with allits layers finished, secured by a coil of compression tape that can beremoved subsequent to curing, and

FIGS. 16, 17, and 18 illustrate further embodiments of shapes accordingto the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, an initial lamination in the form of an innersupporting layer 1 of glass fibers, glass cloth, glass knit, or glassplait is stretched over or wrapped around a positive mold, which is notillustrated in FIG. 1. The layer 1 which is illustrated in FIG. 1 is aplait. Another lamination in the form of a shell layer 2 consisting ofparallel carbon fibers is laid over the inner supporting layer 1. Bothlayers may be impregnated with plastic resin and initially curedtogether. The parallel carbon fibers are connected with strips 20 ofadhesive tape when the shell layer 2 is applied, facilitating itsapplication to the inner supporting layer 1.

Although the inner supporting layer 1 can be a tubular plait, it canalso be formed into a tube by butting its edges together or coiling itaround the mold. Its intimate connection to shell layer 2 will provideadequate stability in any of these three cases.

Inside the wall 30 of shape 3 is a cellular-core layer 4, which can bemultiple and preferably double as illustrated. In the embodimentillustrated in FIG. 1 it is a unit and has a connective layer 40 in themiddle. Connective layer 40 can be made plastic, foil, glass cloth,non-woven carbon-fiber fabric, polyamide, or woven or non-woven fabricimpregnated with plastic resin. It can be impregnated with a plasticresin. Connective layer 40 connects two cellular-core layers, an innercellular-core layer 41 and an outer cellular-core layer 42. As isevident from FIG. 1, the cells of the double or multiple layer can be ofdifferent sizes and heights. Cellular-core layer 4, whether single ormultiple, can enclose the inner supporting layer 1 and shell layer 2with a simple butt joint 43 or, as illustrated by the dot-and-dash linein FIG. 1, be applied in the form of coiled strips 44, in which case thestrips will abut each other.

When a cellular-core layer 4 is present, it is covered by an outerlamination. This is an outer shell layer 5 which again consists ofparallel carbon fibers that can if necessary be held together by hotbonding or by strips 50 of adhesive tape, and of an outer supportinglayer 6, which consists again of glass, fibers, glass cloth, glass knit,or glass plait. The outer supporting layer 6 illustrated in FIG. 1 isagain plaited. The two layers 5 and 6 can also be impregnated withplastic resin and applied wet.

The finished layer structure can be retained with a coil 7 ofcompression tape, which can be removed after the shape as a whole hascured. This coil consists preferably of a polyamide tear-off tape.

Thus, subsequent to laying a first lamination in the form of innersupporting layer 1 and/or shell layer 2 on the positive mold or core andsubsequent to applying a single- or multiple-lamination cellular-corelayer 4, another lamination in the form of outer shell layer 5 and/orouter shell layer 6 is applied.

The structure and composition of the laminations can be varied. It is anadvantage if the supporting layers always consist of glass fibers andthe shell layers of parallel carbon fiber layers are oriented along theaxis of the shape to strengthen it longitudinally to the greatest extentpossible. The inner and outer supporting layers do not absolutely haveto consist of glass fibers. They can consist of aramide or carbon and,as previously mentioned, be applied in the form of a woven or plaitedtube.

The carbon fibers of the inner and outer shell layers can also beapplied in the form of a plaited tube instead of lying parallel when nosupporting layers are present.

As previously mentioned herein, the individual laminated structure aboveand/or below the cellular-core or honeycomb layer can also beconstructed differently.

There is a great advantage to applying a coil of compression tape thatcan then be removed. Not only will the shape retain its form preciselyuntil it has cured, but the laminations will also be compacted, air willbe forced out of it, and the impregnation of the layers will be moreuniform. The coil is pulled tight enough to prevent any air bubbles fromremaining in the laminations because any air inclusions between thelaminations entail a lower load-supporting capacity. Thus the coil issubjected to powerful tension.

If the shape is intended to withstand shearing forces or transversecompression forces later, a double cellular core resulting from thepositioning of a double or multiple cellular-core layer is an advantage.The height and diameter of the cells can also increase from inside out.An impregnated woven or non-woven fabric based on glass and aramide orcarbon fibers impregnated with multiconstituent plastic can also bepositioned as a connective layer between the individual doublecellular-core layers.

FIG. 2 illustrates the construction of a multiple layer with cells ofvarying dimensions. This embodiment has two connective layers 40, acoarser outer cellular-core layer 42 and a finer inner cellular-corelayer 41 in conjunction with an intermediate cellular-core layer 45.This design makes it possible to also wrap the sections of a shape thathave shorter radii. This is especially important when rectangularcross-section tubes like that illustrated in FIG. 1 are manufactured.

FIGS. 3 to 7 illustrate possible steps in the manufacture of a shape inaccordance with the invention. A block-shaped mold 8, made of rigidexpanded polystyrene or a similar material has templates 80 and 81,which preferably have pins 80' and 81' forced into the template materialat each end.

A heated wire 83 is wrapped around the outer edges of templates 80 and81 with tongs 84 as illustrated in FIG. 4. This operation is in itselfknown. The result is a positive mold 88 that can be wrapped into a film89. When, however, the mold is to be later extracted from the finishedshape, a mold release can be applied instead.

A glass-fiber fabric, elastic tube, or similar structure can then bepulled over the resulting positive mold 88 to produce an innersupporting layer 1 as illustrated in FIG. 5. A shell layer 2 of parallelcarbon fibers is then applied either directly, impregnated with amulticonstituent plastic resin, or subsequent to a cellular-core layer 4as illustrated in FIG. 6.

Over this in any case is a supplementary or unique cellular-core layer4, which may be single, double, or multiple.

On top of this intermediate cellular-core laid 4 is layed another seriesof carbon fibers to form an outer shell layer 5 as illustrated in FIG.7, over which a supporting layer 6, preferably of glass fibers, is thenpulled. This can also be impregnated and also with a multiconstituentplastic resin. The shape will be finished once it has cured.

FIGS. 12 and 13 illustrate other types of shapes 3 that can be somanufactured.

FIGS. 8, 9, 9a and 10 illustrate various embodiments of a cellular-corelayer. They are preferably only a few millimeters thick, 5 mm thick forexample, when applied as a single layer.

Various types of cellular-core layers can be manufactured. They can bemade of plastic, specifically from extruded sections of a rapidly curingmaterial. This section, in which the cells are forced out of theextruder axially, is then cut into plates or disks of an appropriatethickness. It is, however, also possible to make the cellular-core layerout of individual sheets of plastic or aluminum appropriately cementedtogether.

The individual cells can preferably be hexagonal, as shown in FIG. 9,inasmuch as the hexagon is especially practical when the material ismade of separate sheets. The cells can, however, also be round, asillustrated in FIGS. 8 and 10, when the material is extruded,

FIG. 11 is a section through a double layer. The upper cells have alarger diameter and are higher than the lower cells. The layer can alsovary in thickness. The structure of the upper cellular-core layer isselected in accordance with the desired final shape. Layers that vary inthickness can be employed to make the surface of a shape, a tubularsection for example, undulate, with the thinner areas of the layerwrapped around the edges, because it is easier to structure an edge witha thinner area, as illustrated in FIG. 2. The surface of such a doublelayer will accordingly be wavy.

FIG. 9a shows cellular material other than the cellular-core material.The cellular material is a rigid foam of polyurethane, polyvinylchloride, polyacrylic, polystyrene, epoxide, polyethylene, or polyester.The rigid foam can be closed- or open-pored or closed- or open-celled,preferably medium-pored. It can be in sheets or strips and processedlike the honeycomb layer. It can also be introduced in the foam ofliquid components and only foamed in situ into or onto the semifinishedshape.

FIG. 14 illustrates the final product 3 of the process illustrated inFIGS. 3 through 7. FIG. 15 illustrates how this product can be providedwith a coil 7 of compression tape that can be removed subsequent tocuring.

This coil can, as previously mentioned herein, be a strip of polyamidetear-off tape if necessary. It is applied with its edges overlappingsubject to powerful pressure and helps to ensure the desired finalshape.

It is also possible to leave the positive mold 88 inside in the shape 3and even bore a hole through it to manufacture a rotating shape asillustrated in FIG. 16.

FIGS. 17 and 18 illustrate further embodiments of shapes that can bemade according to the invention. FIG. 17 illustrates two attachedtruncated cones and FIG. 18 shows a shape with a varying rectangularcross-section. FIG. 18 also illustrates how the surface of a shape canbe made to undulate.

The double or multiple layer can be manufactured and applied as a unit.The double or multiple layer can also be produced while the shape isbeing manufactured. The diameter, height, and configuration can bevaried in accordance with the purpose for which the shape is intended.The dimensions of the cells can increase from the positive mold outward.If the cells are constructed from sheets cemented together, they shouldbe wrapped into a lamination in a helix with their edges in contact.They can, however, also be applied in a spiral, with the end of thespiral flattened to prevent steplike irregularities in the surface ofthe shape. The spiral would preferably extend over the total length ofthe device, preferably in complete coils over the outer surface. Atleast one, also spiral, lamination would also be inlayed confinedbetween the spirals and could function as a connective layer 40. Asingle connective layer consisting of a woven or non-woven fabric canalso be placed between the spirals as illustrated in FIG. 17.

The shell layer 2 or 5 generally illustrated in most of the figuresconsists of parallel carbon fibers connected by strips 20 or 50 ofadhesive tape. The laminations can be modified in a very large number ofdifferent ways, the cellular-core layer, however, remaining of specialsignificance because it makes the shape more stable and, especially,flexurally stronger.

Other materials, like rigid expanded polystyrene for example, can alsobe employed for the positive mold. Any desired appropriate plastic canin fact be employed. The positive mold can also be a steel arbor that isexpelled once the shape has cured. A glass tube can also be used for thepositive mold if necessary and removed after being broken once the shapehas cured. The last stage of the procedure can also be variedaccordingly.

The characteristics disclosed herein are to be considered individuallyand in combination as essential to the invention to the extent that theyare innovative with respect to the state of the art.

It will be appreciated that the instant specification and claims are setforth by way of illustration and not limitation, and that variousmodifications and changes may be made without departing from the spiritand scope of the present invention.

What is claimed is:
 1. A method of manufacturing a shape from acomposite material on a positive mold, comprising the steps of applyingaround the mold laminations which are impregnated with plastic resin andinclude reinforcing fibers, said fibers being at least substantiallyparallel to each other in at least one of the laminations; and embeddingat least one cellular-core layer of rigid foam into a neutral zone ofthe laminations while the laminations are being built up, said layerconstituting at least one strip which is embedded in the neutral zone inthe form of a helix.
 2. The method of claim 1, wherein said embeddingstep includes embedding into the neutral zone at least two neighboringcellular-core layers.
 3. The method of claim 2, wherein the cells of thelayers have different sizes and the larger cells are more distant fromthe mold.
 4. The method of claim 2, further comprising the step ofembedding a connective layer between the neighboring cellular-corelayers.
 5. The method of claim 4, wherein the connective layer iscomposed of materials selected from the group consisting of foil,plastic, glass cloth, non-woven carbon fiber fabric, polyamide, wovenfabric impregnated with plastic resin and non-woven fabric impregnatedwith plastic resin.
 6. The method of claim 1, further comprising thestep of converting the layer into a tube prior to said embedding step.7. The method of claim 1, wherein the edges of neighboring convolutionsof the helix abut each other.
 8. The method of claim 1, furthercomprising the step of inserting a spiral between the convolutions ofthe helix.
 9. The method of claim 1, wherein said applying step includesplacing a first lamination around the mold and said embedding stepincludes placing the layer around the first lamination, said applyingstep further including placing a second lamination around the layer. 10.The method of claim 9, wherein the second lamination includes severalstrata.
 11. The method of claim 9, wherein the first lamination iscomposed of (a) a supporting layer of glass fibers, glass cloth, glassknit or glass plait and is stretched over or wrapped around the mold and(b) a second layer consisting of parallel fibers surrounding thesupporting layer, the second lamination including an outer layer ofparallel fibers.
 12. The method of claim 1, wherein the plastic resin iswet during application of lamination around the mold.
 13. The method ofclaim 1, wherein the mold consists of plastic-coated foam.
 14. Themethod of claim 1, wherein the fibers are parallel to each other andfurther comprising the step of applying transverse strips of adhesivetape to the parallel fibers prior to the application of such fibersaround the mold.
 15. The method of claim 1, wherein the mold has apolygonal outline.
 16. The method of claim 1, wherein said embeddingstep includes introducing the layer between the laminations in suchorientation that the cells of the layer are disposed radially of theaxis of the shape.
 17. The method of claim 1, wherein said embeddingstep includes simultaneously introducing into the neutral zone at leasttwo preformed layers.
 18. The method of claim 1, wherein the layer hasan undulate surface.
 19. The method of claim 1, further comprising thesteps of making the layer from an extruded sheet-like flexible materialand subdividing such material into sheets prior to said embedding step.20. The method of claim 1, wherein the layer is a rigid foam selectedfrom the group consisting of polyurethane, polyvinyl chloride,polyacrylic, polystyrene, epoxide, polyethylene and polyester.
 21. Themethod of claim 20, wherein the layer is foamed in situ.